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Re: Dead computer after system shutdown. - Resolved for Now




On Sunday 06 May 2018 23:10:54 Cindy-Sue Causey wrote:

> On 5/6/18, rhkramer@xxxxxxxxx <rhkramer@xxxxxxxxx> wrote:
> > On Sunday, May 06, 2018 04:57:13 PM tomas@xxxxxxxxxx wrote:
> >> On Sun, May 06, 2018 at 09:19:24PM +0200, Hans wrote:
> >>
> >> [...]
> >>
> >> > Check also the elkos, if they are blown thick, they are also a
> >> > problem.
> >>
> >>                  ^^^^^ electrolytic capacitors, for you non-German
> >> speakers
> >>
> >> :)
> >
> > Thank you!
>
> Ditto because a quick Internet search is primarily bringing up pens.
> That would have been a head scratcher where I'd have been wondering
> what inference was being missed. :)
>
> Cindy :)

Same here Cindy, and I've been chasing electrons to make them do usefull 
things for very close to 70 years.

FWIW, its been 55 of those years since I last saw a Telefunken radio so I 
have no clue what safety pressure release mechanism is used by the 
German speakers electrolytics today, but on our side of the small pond 
that laps at out right coast, the cans are scored on top so that they 
can finish the crack and relieve the pressure in a more or less 
non-destructive manner, but the tops will often visibly bulge quite a 
bit in the earlier stages of such a failure, so we look for domed tops 
as an indicator that *ESR is raising its ugly head in the power circuits 
and trouble is not far off.

Because these capacitors can get rid of heat thru the leads soldered to 
the mainboard as the majority of is it generated by the other end of the 
lead inside the capacitor, those areas of copper are often huge in 
comparison to a normal pcb trace so they can act as a heat sink.  And it 
can take enough heat to physically damage the board to actually free the 
failed capacitors from the board, get the thru holes cleaned out and new 
capacitors re-installed. IBM's mainboards are famously difficult to 
rework in that area.  And they got burnt by the bad caps a few years 
back just as badly as the cheap boards.

ESR*, Equivalent Series Resistance, the resistance of a capacitor when 
measured by a high frequency AC signal, typically 50 to 100 kilohertz.

This is very important in modern switching supplies, and a reading above 
2.5 ohms for a 100 u-f capacitor is enough to give it a new home in the 
trash can. Correspondingly lower for the larger capacitors.

Your trivia factoid for the evening. :)
-- 
Cheers, Gene Heskett
--
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page <http://geneslinuxbox.net:6309/gene>